Solar powered systems provide benefits such as reduced installation cost, the ability to be installed in areas where no other source of energy is available, etc. Typically, a solar powered system will consist of a solar panel, battery, load (such as a light emitting diode) and associated circuitry. The associated circuitry controls charging of the battery, load operating times and load operating levels.
Sizing of the solar panel or panels, battery or batteries for a given installation requires many inputs for optimal cost for a given performance requirement. For instance, the latitude and weather conditions in a given installation location significantly affect the amount of power available to the system. In addition, if the location of installation can be shaded by buildings, trees, etc., it may be desirable to reduce the load levels, load operating times, increase the size of the solar panel, increase the size of the battery, etc. in order for continued operation of the device.
Solar powered systems may be used in many different applications. These applications include marine beacons, aviation beacons, roadway signals, transit shelter lighting systems, roadway signs, etc. Some applications have known operating times which may be taken into account during the design of the system. Other applications have operating times that are determined by the user of the system. When the operating times are determined by the user, design of the system becomes more difficult because the amount of energy used by the system over a given time period may be unknown at the time of design or installation of the system.
A solar power lighting system may have to be designed to provide adequate energy to the lights during the winter when the amount of solar insolation may be reduced. This may be more of a consideration for latitudes farther from the equator as day length is reduced by a greater amount during the winter than at latitudes closer to the equator. Typically a combination of sizing the solar panel to provide enough energy in the winter months and sizing the battery to carry adequate energy through the shortest days of the year is used to ensure adequate lighting. For lighting systems designed to provide light primarily during the night, the effect of shorter days with less solar insolation is compounded by the fact that the nights are longer in the winter. Thus, the lighting system requires more energy. The solar panels and batteries are often sized for sustained winter operation; therefore during the summer months, an excess amount of energy is available from the solar panels and/or batteries which typically cannot be utilized.
In some solar powered lighting applications, it may be desirable to control the lighting based on the time of day. Since solar powered lighting is often installed in areas where access to communications infrastructure is limited, maintaining the time of day using conventional means such as through wired or wireless communications may be difficult.